Graphic Design college courses taught me different. I've had it bludgeoned into my head for 2 years to always use PNG, bonus points if people get creative with transparencies in comic pages. (Which I plan to in the future. Won't be visible here on Tap with the white background but it would be on DA on the grey.)
There IS a way to compress JPG's without artifacts, though! It frankly depends on individual people's sized canvases, art styles, and general work technique as to whether it would work or not. You can also save file images (including PNG's) at "lowest compression" option when saving an image that auto-compresses it without artifact damage, too, in case anyone didn't know that. .o But yeah, JPGs are smaller. Frankly I think it really really REALLY depends on how folks's comics are made.
For instance. I use Bitmaps to make my pages look like they're screentoned. If I were to do JPGs, and it had ANY level of artifact on it anywhere, you'd most definitely see. It'd blur out the Bitmap and look godawful. I couldn't do it even if I wanted to, HOWEVER, my canvas sizes are relatively small (I don't need huge huge huge canvases, tho I still shrink down my images when done!) so my file sizes have never given me a problem on PNG saved format. .x So, like I said, it depends.